There are known different systems for measuring internal pressures in pipe systems. U.S. Pat. No. 4,425,800A discloses a device for ascertaining the internal pressure in a pressure system, particularly in a fuel injection pipe system, wherein the pressure to be measured is contained within an element which includes at one point a wall portion of reduced thickness so as to act like a membrane, and wherein a sensor device is included which is positionable in engagement with the membrane-like wall portion to detect any elastic deformation and variation of the membrane caused by the influence of the internal pressure.
So, by U.S. Pat. No. 4,425,800A the use of sensors located at points of the pipe that have the potential to suffer a deformation by the fluid contained in the pipe is already known. However, reducing the thickness of the wall of the pipe entails certain skill and could give rise to problems, going from measuring problems to leaking problems, depending on how much the thickness is reduced. Also, such reference does not address remote measurements with electrical current generation limitation.
German patent application DE19813756A discloses a method for measuring the pressure of a fluid. The fluid is applied to a measuring object so that the pressure of the fluid deflects a mechanical pick-up measuring element, which is part of the measuring object. The movements of the pick-up element are of a membrane type and its deflection is measured using at least one sensor placed at the furthest side from the fluid. The pick-up element is formed by at least one blind hole perpendicular to the side of the measuring object nearest to the fluid. The Application does not solve the air trapping problem and, again, the Application does not address remote measurements with current limitation.
In aeronautical field also exists the need of measuring the pressure exerted by a fluid within a pipe. Specially, this need arise for the fuel pipes of the aircraft fuel tanks, since monitoring the pressure of the fuel is an essential issue for aircraft testing operations.
International airworthiness regulations are very restrictive regarding the installation of electrical devices within aircraft fuel tanks, since the electrical current in the fuel tank of the aircraft is limited. Therefore, in order to comply with the international airworthiness regulations, the fuel pipes inner pressures must be remotely measured.
FIG. 1 shows a schematic representation of a prior art aircraft fuel installation wherein a fuel pipe 17 crosses the installation and runs within an aircraft fuel tank compartment 16. Due to the electrical current restriction, the fuel pipe 17 pressure is measured outside the aircraft fuel tank compartment 16 by a sensor 20 connected to the fuel pipe 17 via a small diameter pipe 18. The small diameter pipe 18 is connected, at one side, to the fuel pipe 17 and, at the other side, to the sensor 20 and is responsible for measuring the inner pressure of the fuel pipe 17. The small diameter pipe 18 achieves measuring the fuel pipe 17 pressure at the point 19 where the pressure has to be measured, and helps to comply with the electrical current limitation allowing placing the sensor 20 out of the aircraft fuel tank compartment 16. This sensor 20 is usually placed on the compartment wall.
However, in many cases, the point to be measured is at a long distance from the closest compartment wall, so that the small diameter pipe has to cover a large route. In these cases, the fuel installation becomes complicated, especially when the route runs close to some accesses, which have to be cleared, or close to some hardware that has to be avoided.
Additional drawbacks may come up if the small diameter pipe has a route with high points or if the fuel pipe is not well primed, in these cases, the small diameter pipe might trap air. Trapped air within the small diameter pipe disturbs the pressure measurement, since it operates as a sensing pipe. These disturbances are more significant during transients, making measurements completely invalid.
Therefore, it has been detected in this technical filed the need for a system for remotely measuring pressure that provides a reliable measure of pressure and that avoids trapping air. Additionally, it has been detected that this system is especially needed in the aeronautical industry in order to fulfill with the international airworthiness regulations and perform remote measurements of the pressure of the fuel pipes that run within the aircraft fuel tank compartments.